Using a notepad i cut the hex file into two .
pgm1.hex ( address < 4k , 0-0FFFh)
pgm2.hex ( adress > 4K , 1000h and above)

To me, it this method seems wrong. Where is the first file's Endo of file marker?
Have a close look at Intel HEX file format( which is in Turorials, I think)

Also if the device has been locked (all 3 bits) then external execution is disabled as well.